This invention relates to industrial milling apparatus for grinding or milling small solid particles contained in liquid, and more particularly relates to an improved rotor disc which agitates a grinding media as the liquid is pumped through a milling vessel.
Sand milling is a proven, practical, continuous, high-production method of dispersing and milling particles in liquid to produce smooth, uniform, finely dispersed products. One good example of this is the disbursement of pigment agglomerates in paints. The process is also applicable to the wide variety of inks, dye stuffs, paper coatings, chemicals, magnetic tape coatings, insecticides and other materials where millings of a high degree of fineness is required.
In a typical sand milling process, the material or slurry to be processed is introduced at the bottom of the processing chamber or vessel and pumped upwardly through a grinding media, which used to be sand, but is now more commonly small diameter metal shot, manufactured grit or glass beads. A rotor including a shaft and a series of discs positioned within the vessel mills the slurry as it is pumped through the media.
The rotor discs have typically been generally flat disc-like elements having axially extending holes through which the liquid moves when being processed through the vessel. It can be appreciated that the grinding media which reduces the size of the particles in the liquid pumped through the vessel also is very abrasive on the rotor discs. Typically, the discs have been made of a specially hardened metal such as chrome 250 alloy to enhance wearability. Nevertheless, the continuous rotation of the rotor discs gradually wears away the disc material making them thinner and thinner until the outer rim or periphery of the disc actually wears to a knife edge.
Thus, it is desirable that the life of the rotor discs be extended. Replacement of rotor discs includes not only the cost of the discs themselves but the substantial amount of labor required, as well as the lost operational time of the apparatus.
It is also always desirable to improve the efficiency of the milling operation.